1. Field of the Invention
The invention relates to insulating glazings composed of at least two glass sheets separated from one another by a small space in which a vacuum has been produced.
2. Discussion of the Background
To obtain a thermal and/or acoustic insulation it is customary to form insulating glazings comprising two glass sheets separated from one another by a relatively large air space. Such glazings provide a thermal insulation that is judged insufficient for certain applications. To remedy this, it is known to make glazings that comprise three glass sheets, with one of the air spaces being able to be replaced with a gas, for example krypton. These glazings have thermal insulation properties that are clearly improved, but are of such a thickness that it is not always easy to use them.
Furthermore, users' current demands are directed toward a thermal insulation of glazings equivalent to that of solid partitions or walls.
Insulating glazings made of two glass sheets separated from one another by a space in which a vacuum has been produced have also been proposed, for example in patent WO 91/02878. As a result of the vacuum, these glazings have very good insulating properties, but they are very difficult to produce. On one hand, the small thickness between the two glass sheets, which is a few tens of millimeters, must be constant over the entire area where the glass sheets are facing. On the other hand, sealing of the two glass sheets must be made perfectly fluidtight.
Patent WO 91/02878 describes a technique which includes placing pins of several tens of millimeters thick on one of the glass sheets such that the pins are distributed over the entire surface, and also providing a joint which will permit the sealing of the two sheets. These pins and this joint are made of the same material of a glass composition. It appears that this glazing is difficult to produce because of these simultaneous required operations which are quite delicate. In addition, the sealing joint exhibits a number of bubbles which can be detrimental to fluidtightness or to attractiveness.
The above patent also describes a process for producing the vacuum between the two glass sheets. In particular, it proposes inserting a tube between the two glass sheets before sealing, to which a connection is made to pump out the air. Another embodiment consists in drilling a hole through one of the glass sheets and pumping the air through this opening. In the first case, it is necessary to seal the tube in a fluidtight manner at the same time as the glass sheets, which makes the operations difficult. Furthermore, after having produced the vacuum, it is necessary to seal the end of the tube, then protect this end to prevent it from breaking. In the second case, the vacuum is produced by a tube previously sealed around the hole. Then after having produced the vacuum, this tube is melted so as to seal its end. The drawback of these embodiments is the resultant insulating glazing exhibits a brittle point or break point (fragile region) either on the periphery, or on a surface thereof. In the second case there is, in addition, a part of the tube disposed outside of the glazing, which increases the danger of damage.